fix(internal/gapicgen): handle deleted files in git history

internal/gapicgen/generator/generator.go

@@ -21,6 +21,7 @@ package generator
 import (
 	"context"
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"sort"
@@ -86,7 +87,18 @@ func gatherChanges(googleapisDir, genprotoDir string) ([]*git.ChangeInfo, error)
 			if !strings.HasSuffix(file, ".proto") {
 				continue
 			}
-			pkg, err := goPkg(filepath.Join(googleapisDir, file))
+			content, err := git.GetFileContentAtCommit(googleapisDir, commit, file)
+			if err != nil {
+				// It's possible the file was deleted in this commit, so we check the parent.
+				originalErr := err
+				content, err = git.GetFileContentAtCommit(googleapisDir, commit+"^", file)
+				if err != nil {
+					// We don't want to fail here, just log the error and continue.
+					log.Printf("could not get content for %s at commit %s (%v) or its parent (%v)", file, commit, originalErr, err)
+					continue
+				}
+			}
+			pkg, err := parseGoPkg(content)
 			if err != nil {
 				return nil, err
 			}

internal/gapicgen/generator/genproto.go

@@ -220,14 +220,9 @@ func filterPackages(in map[string][]string) (map[string][]string, error) {
 	return out, nil
 }
 
-// goPkg reports the import path declared in the given file's `go_package`
-// option. If the option is missing, goPkg returns empty string.
-func goPkg(fileName string) (string, error) {
-	content, err := os.ReadFile(fileName)
-	if err != nil {
-		return "", err
-	}
-
+// parseGoPkg parses the import path declared in the given file's `go_package`
+// option. If the option is missing, parseGoPkg returns empty string.
+func parseGoPkg(content []byte) (string, error) {
 	var pkgName string
 	if match := goPkgOptRe.FindSubmatch(content); len(match) > 0 {
 		pn, err := strconv.Unquote(string(match[1]))
@@ -242,6 +237,16 @@ func goPkg(fileName string) (string, error) {
 	return pkgName, nil
 }
 
+// goPkg reports the import path declared in the given file's `go_package`
+// option. If the option is missing, goPkg returns empty string.
+func goPkg(fileName string) (string, error) {
+	content, err := os.ReadFile(fileName)
+	if err != nil {
+		return "", err
+	}
+	return parseGoPkg(content)
+}
+
 // protoc executes the "protoc" command on files named in fileNames, and outputs
 // to "<genprotoDir>/generated".
 func (g *GenprotoGenerator) protoc(fileNames []string) error {

internal/gapicgen/git/git.go

@@ -202,3 +202,14 @@ func FilesChanged(gitDir, hash string) ([]string, error) {
 	}
 	return strings.Split(string(b), "\n"), nil
 }
+
+// GetFileContentAtCommit returns the content of a file at a specific commit.
+func GetFileContentAtCommit(gitDir, hash, filePath string) ([]byte, error) {
+	c := execv.Command("git", "show", fmt.Sprintf("%s:%s", hash, filePath))
+	c.Dir = gitDir
+	b, err := c.Output()
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}